Such apparatuses are used for example in motor vehicles in drive systems for window winders, sunroofs and also in sliding doors, tailgates and the like, to detect the position, speed or direction of movement of the motor and therefore of the driven component. Hall sensors for example, as well as optical coders, capacitive and inductive sensors and the like can be used as sensors, generally quadrature encoders. Lines have to be installed for such sensors, specifically for their voltage supply, as for the output signals, said lines being passed by way of cable harnesses to a control unit. The sensors here can either be integrated in the motor or can also be embodied as so-called stand-alone sensors. The lines in such a system incur costs, the costs increasing with the number of lines. The cable harnesses located in the vehicle increase the weight of the vehicle. Also the maximum possible diameter for the execution of cable harnesses is limited, for example by a vehicle door in the vehicle chassis. Also the additional line in a cable harness increases the probability of failure, for example because of the plug-in contacts required in the vehicle. This has the further disadvantage that each line connection entails a technical risk, as each line is sensitive to interference.
Different routes have been followed in the past to supply power to sensors and to extract sensor signals, as shown in FIGS. 1 to 4, all of which show solutions according to the prior art.
FIG. 1 for example shows a double sensor unit 1, which is known per se and comprises two sensors A, B, the output signals of which are applied to outputs 1A and 1B by way of transistors TA and/or TB and resistors RA and/or RB. Two lines are also required to supply power, namely a common power supply line VBATT and a common ground line GND. With this embodiment the data signals at the outputs 1A and 1B contain the full information content relating to the position and speed of the electric motor, i.e. more precisely of the rotor of such an electric motor. A—conventional—electronic analysis system (not shown), which is connected to the outputs 1A and 1B, can therefore always detect the motor position and speed for example correctly.
FIG. 2 shows a speed/direction sensor unit 2, which in turn comprises two independent sensors A, B, which are applied here by way of a logic module 2AB with comparable output transistors TS, TD and resistors RS and/or RD to outputs 2S and/or 2D. The logic module 2AB analyzes the position signals of the sensors A and B directly to obtain a speed signal S and a direction signal D, with corresponding speed and/or direction signals being output at the outputs 2S and 2D. A power supply line VBATT and a ground line GND are also present here for voltage supply purposes, in other words a total of four lines. It is possible to detect the required parameters here too in respect of a standard electronic analysis unit.
One disadvantage of the two known embodiments is that a total of four lines are required, resulting in the disadvantages listed in the introduction.
In the embodiments according to FIGS. 1 and 2 the resistors RA, RB and/or RS, RD, which are connected in series to so-called open collector outputs of the transistors TA, TB and/or TS, TD, protect the sensor outputs from a short circuit to VBATT.
As a modification of the embodiment according to FIG. 1 it has already been proposed, see FIG. 3, that in a comparable dual sensor unit 1′ the two sensor output signals should be modulated as two out of phase square signals onto the supply currents of the sensors A, B of the sensor unit 1′. Independent power supply lines VBATT_A and VBATT_B are therefore provided for the two sensors A, B and the respective square signals, i.e. high/low level, are modulated onto the supply currents carried by way of these lines, this being possible for example with the aid of the resistors RA, RB. The two resistors RA and RB can be identical here, i.e. RA=RB=R.
Instead of by way of resistors, current modulation can however also take place in the conventional manner by way of power sources.
Here too the data signals contain the full information content relating to the position and speed of the motor, so that the electronic analysis unit can always detect the corresponding parameters correctly but three lines are still required for this sensor unit 1′.
FIG. 4 shows a variant of a sensor unit 3 with just two lines VBATT_A and GND, with in this instance only a single sensor A being contained in the sensor unit 3. The—single—sensor output signal can for example be modulated in turn by way of a transistor TA and a resistor RA onto the supply current on the power supply line VBATT_A, and the ground line GND is present as the second line.
Alternatively the output line VBATT_A, which is connected directly to the resistor RA, could be replaced by a specific data output line 3A and a separate power supply line VBATT could be provided, as shown with a broken line in FIG. 4. In the latter instance three connecting lines would be necessary, in the first two connecting lines. However the variant according to FIG. 4 has the disadvantage that the output data signal no longer contains the full information content relating to position and speed. An electronic analysis unit can therefore only detect the position of the motor partially correctly and runout and reverse estimators are necessary to try to estimate the correct position. If for example in the case of a non-actuated motor edges occur on the sensor output line VBATT_A or 3A, it is only possible to assume the direction of movement. The requirements for system self-locking are also very stringent.